JP2002088494A - Method for recovering platinum group metal from metallic electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of separating and recovering platinum group metals from used insoluble metallic electrodes at high purity by peeling and separating coating layers containing platinum group metal oxides from the metallic electrodes, then removing most of impurities from the coating sludge. SOLUTION: In recovering the platinum group metals from the used insoluble metallic electrodes having the coating layers containing the platinum group metal oxides, the coating layers are physically and/or chemically stripped from electrode base materials. The coating material sludge is heated in a reducing atmosphere to reduce the platinum group metal oxide components to metals and thereafter these metals are chlorinated. The undissolved portions are filtered away in the state of the aqueous hydrochloric acid solution and are then subjected to the separation and removal of the existing cations by an electrodialysis method, by which the high-purity platinum group metals removed of most of the impurities are recovered in the form of chlorides.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering a platinum group metal from a metal electrode, and more particularly to a method for recovering a platinum group metal oxide which has been used in industrial electrolysis and mainly used as an electrode material. The present invention relates to a method for recovering a platinum group metal from an insoluble metal electrode provided on an electrode substrate.

[0002]

2. Description of the Related Art A so-called dimensionally stable anode (DSA) and a dimensionally stable electrode (DSE) having a coating layer of an electrode coating containing a platinum group metal oxide such as iridium or ruthenium on a titanium electrode substrate. The so-called insoluble metal electrodes are used in large quantities in various electrochemical fields, such as diaphragm electrolysis. Such a metal electrode is a ceramic whose surface coating layer is stable, but has a certain chemical bond with the titanium electrode base material, and is extremely stable physically and chemically. It is known that in this way,
Even if it is stable as a metal electrode, it will gradually wear out due to corrosion etc. over a long period of use, and it will not be possible to maintain a certain level of performance with a certain amount of surface coating layer left, making it unusable and eventually being disposed of The Rukoto.

[0003]

However, as described above, it is quite difficult to recover a metal or a coating layer from a metal electrode made of, for example, titanium, which is extremely stable physically and chemically. At present there is no method. That is,
Platinum group metal oxides are much more stable in terms of chemistry than platinum group metals, so only certain special treatment methods, such as alkali melting, can be used. Since the group metal oxide electrochemically protects the surface of the electrode substrate, it is extremely difficult to separate the coating layer from the electrode substrate.

[0004] The inventors of the present invention have developed a coating layer containing a platinum group metal oxide on the surface while protecting a titanium electrode substrate by utilizing the fact that the platinum group metal oxide is dissolved in an alkali molten salt. A high-concentration aqueous alkali solution is applied to the surface of the electrode substrate so as to dissolve it, and is heated in a furnace to evaporate the water and to make the alkali substantially in a molten state, thereby forming the coating layer in the alkali. Has been developed for practical use, which is to dissolve in water. However, this method has problems in that it is practically difficult to recover expensive platinum group metals and that large processing equipment is required. Although no problem arises when the electrode substrate is used as it is, it is practically almost impossible to recover both the electrode substrate and the coating layer containing the platinum group metal oxide.

In order to peel off the coating layer, a method has been proposed in which the surface of the electrode substrate is dissolved with a corrosive acid to peel off the coating layer from the electrode substrate (for example, JP-A-59-12).
No. 3730). However, although this method is theoretically possible, the actual problem is that the coating layer does not peel off as expected because the oxide interposed between the titanium electrode substrate and the coating layer is strong. In addition, the recovery rate of the electrode substrate (titanium) is poor. Further, there remains a problem that the amount of acid used is extremely large and uneconomical. In addition, the acid containing the dissolved electrode base material contains a coating sludge of platinum group metal oxide, and the concentration of the noble metal oxide becomes relatively small. He also had the problem of being difficult.

[0006] In the recovery of the electrode substrate, titanium cannot be regenerated unless the coating layer made of ceramic is completely removed, but conventionally, it cannot be completely peeled off. It can be used only as a low value-added alloy material (iron alloy), and has the problem that its value is reduced.

Further, when viewed from the electrode side, it is desirable that the titanium material, the platinum group metal for the coating, or the raw material for the oxide thereof have substantially no history in the past, and the handling is easy. The use of new dissolved titanium is ultimately inexpensive and easy to handle, and is not satisfactory with the conventional method.

[0008] In the past, redistribution of waste pure titanium as titanium has been scarcely carried out because it is difficult to completely remove deposits on the surface. However, in order for expensive titanium to be used like aluminum in the future,
Recycling for recovering titanium from used titanium or titanium alloy metal electrodes is industrially important. To this end, the emergence of a treatment method that separates the electrode substrate and the coating layer from the surface of the titanium or titanium alloy electrode substrate to completely remove deposits such as the coating layer from the surface of the electrode substrate at low cost will be developed in the future. Will be greatly affected.

The present invention has been made in view of such a conventional situation, and an object thereof is to remove a platinum group metal from a used water-soluble metal electrode having a coating layer containing a platinum group metal oxide. An object of the present invention is to provide a method capable of separating and collecting a platinum group metal with high purity by removing a coating layer from an insoluble metal electrode, separating the coating layer from the insoluble metal electrode, and removing most of impurities from the coating sludge.

[0010]

To achieve the object, the present invention provides a method for recovering a platinum group metal from a spent insoluble metal electrode having a coating layer containing a platinum group metal oxide. The coating layer is peeled off from the electrode substrate made of titanium or a titanium alloy or other noble metal, and the coating layer is heated in a reducing atmosphere to reduce the platinum group metal component to the metal. Thereafter, the undissolved portion is removed by filtration, and then the existing cation is separated and removed by an electrodialysis method using a cation exchange membrane, whereby the platinum group metal is recovered as chloride.

In the present invention, the coating layer is peeled off from the electrode substrate physically and / or chemically.

In the present invention, the reducing atmosphere is a hydrogen gas atmosphere, and the preferable heating temperature is in the range of 500 to 1000 ° C. at which the platinum group metal is reduced, and particularly preferably 600 to 1000 ° C.
It is in the range of 950 ° C. The processing time is not particularly limited, but is preferably about 1 to 10 hours, and more preferably 2 to 5 hours.
It is desirable to set it to about time.

Further, in the present invention, when the platinum group metal to be recovered is ruthenium, the chlorination is carried out by dissolving in a heated concentrated hydrochloric acid aqueous solution containing an oxidizing gas.

Further, in the present invention, when the platinum group metal to be recovered is iridium or iridium / ruthenium, chlorination is carried out by heating by mixing with an alkali halide and passing chlorine gas.

In the present invention, the alkali halide is sodium chloride, and the preferable heating temperature is 500 to 700 ° C.
And particularly preferably in the range of 550 to 650 ° C.

Further, in the present invention, electrolysis is performed while supplying a solution to an anode chamber having the cation exchange membrane as a diaphragm, and impurity metals are sent to a cathode chamber to be separated and removed.

Further, in the present invention, the hydrochloric acid aqueous solution of the platinum group metal chloride is concentrated by distillation under reduced pressure.

According to the above technical means of the present invention, when recovering a platinum group metal from a used water-soluble metal electrode having a coating layer containing a platinum group metal oxide, the platinum group metal oxide The coating layer containing the substance from the electrode substrate physically and / or
Alternatively, it is heated in a reducing atmosphere after being chemically stripped.
For example, by heating at 500 to 1000 ° C. in a hydrogen gas atmosphere, a platinum group metal component or the like, which is easy to reduce, is reduced to a metal and then chlorinated, dissolved in hydrochloric acid, and insoluble in the hydrochloric acid aqueous solution. The dissolved portion is removed by filtration, and further separated and removed by an electrodialysis method using a cation exchange membrane with almost no remaining cation. Thereby, high purity platinum group metals are recovered as chlorides.

[0019]

Embodiments of the present invention will be described. As the metal electrode, for example, a coating layer containing a platinum group metal oxide or a composite oxide composed of a platinum group metal and another metal is provided on the surface of an electrode substrate made of, for example, a commonly used titanium or titanium alloy. It is an insoluble metal electrode for industrial electrolysis that is incorporated and used in an electrolytic copper foil manufacturing apparatus, a diaphragm method salt electrolysis apparatus, an ion exchange membrane method chloralkali electrolysis apparatus, or the like. In special cases, the electrode substrate may be nickel or stainless steel, and the electrode in this case is used as a cathode.

In recovering the platinum group metal from the used water-soluble metal electrode used in the present invention, first, a platinum group metal oxide or a composite oxide comprising a platinum group metal and another metal is used. It is separated and collected from the electrode substrate, but this separation is not particularly limited. For example, after applying a physical pretreatment such as damaging the coating layer or rolling the metal electrode itself by rolling or the like to break the bonding state between the electrode substrate and the coating layer, the coating interface of the electrode substrate The coating layer is peeled off from the electrode substrate by performing a chemical post-treatment such as corroding the coating layer with an acid.

Next, the coated sludge (solid sludge) thus peeled is subjected to an acid treatment as it is or to remove a substance which is easily dissolved by an acid. The conditions of this acid treatment are not particularly limited, but for example, 20% boiling hydrochloric acid or 40% or more for removing electrode base materials such as titanium and surface deposits mixed in the coating sludge. Temperature 85
It is desirable to treat with sulfuric acid at a temperature of not less than ℃, and by performing this treatment, metal components other than oxides can be substantially dissolved.

Analysis of the components of the coating sludge made of the electrode material obtained in this way revealed that the coating sludge was mainly composed of valve metal oxides such as titanium and tantalum and platinum group metal oxides. Was. It was also found that some metal components remained as oxides. These metal oxides may be impurities or may be added as electrode materials. However, in order to recover the platinum group raw material without impurities, it is necessary to decompose these as well.

Therefore, in the present invention, the above-mentioned metal oxide is heated in a reducing atmosphere such as a hydrogen atmosphere to reduce the metal oxide to a metal. The reducing atmosphere is not particularly limited. For example, there is a reducing gas atmosphere such as an ammonia gas or a methane gas, but a hydrogen gas atmosphere having the strongest reducibility and having little possibility of contamination is most preferable. The hydrogen gas atmosphere may be a hydrogen gas atmosphere at approximately atmospheric pressure, and the metal oxide is reduced to metal by heating while flowing hydrogen gas. The heating temperature in this hydrogen gas atmosphere is desirably set in the range of 500 to 1000 ° C. at which the platinum group metal is reduced. The reason is that if the temperature is 500 ° C. or lower, the reduction of the platinum group metal oxide tends to be insufficient.
If the temperature exceeds 00 ° C., equipment such as a furnace used for heating becomes large-scale, which causes a rise in processing cost. Another reason is that if a metal other than the platinum group metal is reduced, it may become an impurity as it is, so that the heating temperature at which only the platinum group metal is selectively and preferentially reduced is 500 to 100.
This is because the range is 0 ° C.

Therefore, according to the present invention, in a hydrogen gas atmosphere,
~ 1000 ° C is desirable, particularly preferably 600-950 ° C
Range. At 800 ° C. or higher, an effect is obtained in which at least a part of arsenic and antimony which may be contained as impurities can be removed by evaporation. The processing time in the range of 500 to 1000 ° C. in the hydrogen gas atmosphere is not particularly limited, but about 1 to 10 hours is sufficient, and about 2 to 5 hours is sufficient. By performing the reduction treatment under such conditions, the platinum group metal component which is easily reduced is reduced to a metal, and valve metals such as titanium and tantalum which are hardly reduced are present as oxides without being reduced. . In addition, some of the impurities volatilize and some are reduced to metal. The reduced product in this case dissolves in hydrochloric acid.

In the present invention, when the platinum group metal is iridium or iridium / ruthenium, it is difficult to directly dissolve it in hydrochloric acid. Therefore, the platinum group metal is heated by mixing with an alkali halide such as sodium chloride and passing chlorine gas. Performed by In this case, the heating temperature is desirably set in the range of 500 to 700 ° C. The reason is that the chlorination of the platinum group metal is not sufficient at 500 ° C or less, and the yield tends to decrease.If the temperature exceeds 700 ° C, the reaction proceeds sufficiently quickly, so the problem is that Although the amount is small, the danger increases when the temperature for handling chlorine increases, so that the treatment at the lowest possible temperature is desirable.

For example, the mixture is mixed with an alkali halide such as sodium chloride or the like and chlorinated by passing a chlorine gas while heating to about 600 ° C., and the chlorination is dissolved in an aqueous hydrochloric acid solution. In such a method, most of the platinum group metals can be dissolved, so that they can be recovered, for example, as a mixed chloride containing iridium and ruthenium. At this time, titanium, tantalum oxide and other oxides are separated by filtration as impurities.

In the present invention, when the platinum group metal is mainly ruthenium, chlorination is carried out by dissolving in a heated concentrated hydrochloric acid aqueous solution containing an oxidizing gas. In this case, although it is possible with the above-mentioned method, it is boiled in the air together with an oxidizing agent such as oxygen or chlorine, preferably in an autoclave at 120 ° C.
It can be easily dissolved by using hydrochloric acid heated to a certain degree. In order to facilitate dissolution, it is preferable to use 35 to 37% concentrated hydrochloric acid, which is called so-called 35 hydrochloric acid.

The chlorine gas may be supplied from outside using a chlorine cylinder or the like, but the chlorine gas can be generated and used by placing an electrode in a hydrochloric acid container and performing electrolysis. As the anode at this time, the above-mentioned coated sludge can be used as it is, and the generation of chlorine is minimized and the platinum group metal is dissolved. In this way, the coating sludge dissolves, but the valve metal component which forms a complex oxide such as titanium oxide and tantalum oxide, which is insoluble as an oxide, does not dissolve and remains as sludge. Further, although a small amount of the platinum group metal remains as an insoluble component, they can be recovered separately or added to the next batch to recover all the platinum group metal.

Further, when ruthenium is contained, a part of the waste gas may be volatilized as octavalent ruthenium oxide. Therefore, the waste gas is trapped, and the same is converted to RuCI4 (H2RuCl6) through 35% hydrochloric acid. It can be collected by goods. The platinum group metal thus obtained is dissolved in hydrochloric acid, and the valve metal oxide, which is an insoluble matter, is separated by filtration.

In the present invention, since the platinum group metal solution thus obtained partially contains impurity metals, these are separated and removed by electrodialysis. That is, the hydrochloric acid solution is supplied to the anode compartment of the electrolytic cell separated into an anode compartment and a cathode compartment by a cation exchange membrane, and is energized. Then, impurity metals such as lead and arsenic existing as cations move to the cathode chamber through the cation exchange membrane of the electrolytic cell. As a result, an aqueous hydrochloric acid solution of a platinum group metal chloride remains in the anode chamber. The hydrochloric acid aqueous solution can be recovered as a platinum group metal chloride or chloride solid by, for example, adjusting the concentration of hydrochloric acid or the concentration of platinum group metal by vacuum distillation as necessary.

When two or more kinds of platinum group metal chlorides coexist, they can be separated or, depending on the application, can be recovered as a mixture without being separated.

Next, specific embodiments 1 to 4 will be described in more detail, but it is first described that the present invention is not limited to the embodiments. Example 1 Iridium was recovered from a water-soluble metal electrode having a coating layer containing a composite oxide composed of iridium and tantalum on the surface of a used titanium electrode base material used in an electrolytic copper foil manufacturing apparatus. Was. First, to remove surface deposits from the metal electrode, the metal electrode is immersed in a 1: 1 nitric acid solution containing hydrogen peroxide. Thus, after removing the surface deposits mainly composed of lead oxide, the coating layer was peeled and collected by buffing. Then, in order to remove impurities such as titanium metal which is an electrode base material and stainless steel which is a buffing substance, buffing is performed from the peeled and recovered coating layer.
When the treatment was performed in a 40% sulfuric acid solution at 40 ° C. for 3 hours, it was found that the impurity metal was almost completely removed.

Next, filtration was performed using No. 1 filter paper manufactured by Toyo Roshi Kaisha Co., Ltd., and a large number of solid sludges collected on the filter paper were washed and dried. Further, the solid sludge was placed in a hydrogen furnace to perform a reduction treatment. At this time, the hydrogen pressure in the hydrogen furnace was set to approximately atmospheric pressure, and the processing temperature was set to 800 ° C. When the state of the solid sludge after the treatment was observed by X-ray diffraction, it was confirmed that iridium was a metal and that tantalum oxide and titanium oxide were additionally present. The presence of lead and antimony was also confirmed, albeit in small amounts.

Next, the solid sludge is mixed with the same amount of sodium chloride, then placed in an atmosphere furnace, and allowed to react for 2 hours through a dry chlorine gas while being heated at a temperature of 600 ° C., and then cooled to a 35% hydrochloric acid solution. After dissolution, filtration was performed using the above-mentioned No. 1 filter paper. As the impurity metals, tantalum oxide, tantalum / lead composite oxide, and titanium oxide were confirmed, and slight iridium was confirmed. The hydrochloric acid solution was mainly composed of iridium chloride, but it was confirmed that slight amounts of lead, arsenic, antimony chloride and a large amount of sodium chloride were present.

Next, this product is iridium 150-200 g /
Distillation under reduced pressure was carried out to about l, and it was confirmed that a considerable amount of salt was precipitated. Thus, filtration was carried out with the above-mentioned No1 filter paper, and this filtrate was subjected to electrodialysis. In other words, this filtrate is used as the anolyte for the cation exchange membrane Nafion41.
Electrolysis was performed while supplying the solution to a two-chamber electrolytic cell using 7 as a diaphragm. At this time, a 5% hydrochloric acid aqueous solution was used as a catholyte, an insoluble metal electrode formed by coating iridium oxide on a titanium electrode substrate was used on the anode side, and a anodic current density was used using a niobium plate on the cathode side. Electrolysis was performed at 1 A / dm2 for 10 hours. As a result, it was confirmed that lead and antimony recognized as impurities were removed to the cathode chamber and removed, and sodium was almost completely transferred to the anode chamber. As a result, the impurities in the iridium chloride solution were reduced to a trace level, and could be used as a raw iridium material.

Example 2 A water-soluble metal electrode having a coating layer containing a composite oxide composed of ruthenium and titanium was formed on the surface of a used titanium electrode base material used in a diaphragm method salt electrolysis apparatus. Recovery was performed. First, a treatment with a jet washer was performed to remove surface deposits from the metal electrode. In this way, after removing the surface deposits mainly composed of waste caustic soda and diaphragm material, the coating is peeled and collected by buffing, and the stripped electrode is further washed with 20% hydrochloric acid at 100 ° C together with the collected material. In addition, the remaining coating layer was recovered and the metal component was dissolved. The processing time at this time was 30 minutes.

Next, filtration was performed using No. 5 filter paper manufactured by Toyo Roshi Kaisha Co., Ltd., and a large number of solid sludges collected on the filter paper were washed and dried. Further, the solid sludge was placed in a hydrogen furnace to perform a reduction treatment. At this time, the hydrogen pressure in the hydrogen furnace was set to approximately atmospheric pressure, and the processing temperature was set to 600 ° C. Then put this sludge in a titanium basket and use it as an anode for 100
Electrolysis was carried out in hydrochloric acid at 35 ° C.

On the other hand, a tantalum plate was used as a cathode and placed so as to surround a titanium basket. Electrolysis was performed at a current density of 10 A / dm2, and electrolysis was continued until chlorine gas came out. After stopping the electrolysis when the generation of chlorine gas was confirmed, the electrolytic solution was separated and concentrated by distillation under reduced pressure to analyze the insoluble portion. As a result, approximately 100% of the titanium oxide remained without being dissolved. It was confirmed that ruthenium remained as a solid matter of about 5% of the original amount.

Next, this was concentrated under reduced pressure to adjust ruthenium to about 200 g / l. Then, electrolysis was performed while using this as an anolyte and supplying it to a two-chamber electrolytic cell using a cation exchange membrane Nafion417 as a diaphragm. At this time, 5
% Aqueous hydrochloric acid solution, an insoluble metal electrode coated with ruthenium oxide on an electrode substrate made of titanium as the anode, and a niobium plate as the cathode for 2 hours at a cathode current density of 1 A / dm2. Was. Then, antimony recognized as an impurity was transferred to the cathode chamber and removed, and the impurity in the ruthenium chloride solution was reduced to a trace level and could be used as a ruthenium raw material as it was.

Example 3 On a metal substrate consisting of a perforated titanium plate used in a chlor-alkali electrolysis apparatus using an ion exchange membrane method,
Iridium, iridium from a water-soluble metal electrode having a coating layer containing a composite oxide consisting of ruthenium and titanium,
Ruthenium was recovered. First, in order to remove surface deposits from the metal electrode, a treatment with a jet washer was performed, and then the coating layer was peeled and collected from the electrode substrate by buffing in the same manner as in Example 2.
Pickling was performed by immersion in 40% sulfuric acid. Then, the titanium surface as the electrode base material was corroded by the washing for 2 hours, and the residual coating layer was precipitated as black sludge at the bottom of the pickling tank. The black sludge was taken out from the drain port of the pickling tank and washed with water. The sludge separated and recovered by buffing was then treated for 30 minutes in 20% boiling hydrochloric acid to dissolve and remove titanium and buff metals. Further, this was subjected to a reduction treatment at 650 ° C. for 2 hours in a hydrogen stream.

Next, the reduced product thus obtained was put into an autoclave, heated to 120 ° C. using 35% hydrochloric acid as a solution, and dissolved while passing chlorine gas. As a result, the solution turned black and the insoluble matter precipitated after 3 hours of dissolution. This was taken out and cooled, and then filtered using No. 1 filter paper manufactured by Toyo Roshi Kaisha, Ltd., and a large number of insolubles collected on the filter paper were analyzed. As a result, a small amount of iridium was contained and the remainder was titanium oxide. Was. The solution at this time was a chloride of ruthenium and iridium. This chloride was distilled under reduced pressure and concentrated to a total of about 200 g / l of ruthenium and iridium, and electrodialysis was performed under the same conditions as in Example 2 to separate and remove cations. When the solution after separation was analyzed, trace-level titanium was confirmed in addition to ruthenium and iridium, but other metal ions were not confirmed. This was further distilled under reduced pressure to obtain a mixed chloride of ruthenium chloride and iridium chloride.

Example 4 A coating layer containing a composite oxide composed of iridium, ruthenium and titanium was provided on an electrode substrate composed of a titanium expanded mesh used and used in an ion exchange membrane type salt electrolysis apparatus. Iridium and ruthenium were recovered from the water-soluble metal electrode. First, in peeling and recovering the coating layer from the electrode substrate, the metal electrode is welded, and a large level of strain generated when the metal electrode is removed from the electrolytic device is given to the metal electrode by a strong leveler. By flattening the electrode, a slight gap was formed between the coating layer and the titanium metal substrate, and this was etched by pickling with a mixed acid of hydrochloric acid and sulfuric acid, thereby separating the electrode. At this time, a mixed acid containing 25% as sulfuric acid and 20% as hydrochloric acid was used as an etching solution at a temperature of 85 to 90%.
The above-mentioned flattened metal electrode was kept at ℃ and immersed for 30 minutes. Then, the coating layer precipitated in the liquid as black sludge. At this time, it was confirmed that the coating layer was almost completely removed from the electrode substrate by etching for 30 minutes.

After the black sludge was separated by filtration, washed sufficiently with water and dried, the black sludge was placed in a hydrogen furnace and reduced as in Example 1. However, the processing temperature was 700 ° C. After analyzing the black sludge by X-ray diffraction after the reduction treatment for 3 hours,
This black sludge was found to consist of titanium oxide, iridium and ruthenium.

Next, the black sludge of Example 1 was used.
In the same manner as in the above, the mixture was mixed with the same amount of sodium chloride and chlorinated by passing chlorine gas. At this time, ruthenium tetroxide (RuO4)
Was trapped in 35% hydrochloric acid with 5% isopropyl alcohol by volume.
Then, at the time when the chlorination is completed, dissolve all the chlorides generated in the hydrochloric acid used for the recovery of ruthenium tetroxide, and perform vacuum distillation on this to make a total of about 200 g / l of ruthenium and iridium. Example 1
Electrodialysis was performed in the same manner as described above. Then, the slightly mixed iron almost disappeared, and the presence of other metals was not confirmed. Therefore, it was found that the iron could be used as it was as it was.
The chloride obtained here was a mixture of H2IrCl6 and H2RuCl6, and was found to be almost the same as the composition release coating.

[0045]

The method for recovering a platinum group metal from a metal electrode according to the present invention has the following functions and effects because it is configured as described above. . In the present invention, the coating layer containing the platinum group metal oxide is peeled off from the electrode substrate, and the coating layer is heated in a reducing atmosphere to reduce the platinum group metal component to metal, and then chlorinated.
The undissolved portion is removed by filtration in the state of an aqueous hydrochloric acid solution, and then the cations present are further separated and removed by electrodialysis, so that the platinum group metal is recovered as chloride from the used insoluble metal electrode be able to.

[0046] Further, in the present invention, the coating layer containing the platinum group metal oxide is peeled from the electrode base material by performing physical and / or chemical treatment on the water-soluble metal electrode. It can be easily peeled and separated from the substrate.

[0047] Also, in the present invention, in a hydrogen gas atmosphere 500
By heating the coating layer containing the platinum group metal oxide separated from the electrode substrate in the heating range of up to 1000 ° C., only the platinum group metal component is selectively and preferentially reduced to metal. That is, the platinum group metal component that can be easily reduced is reduced to a metal, and the electrode material that is hardly reduced, for example, titanium, valve metal oxides such as tantalum, etc. is present as an oxide without being reduced. By dissolving this in hydrochloric acid, the platinum group metal component remains in the liquid as chloride, so that the platinum group metal can be easily recovered as chloride.

[0048] Further, in the present invention, since the platinum group metal can be recovered from the coating layer in a form dissolved in hydrochloric acid as described above, after the dissolution, all the recovery is performed by liquid layer treatment, and the handling and recovery are simplified.

[0049] Further, in the present invention, since the metal oxide present in the coating sludge remains as an oxide, it can be easily and easily separated and removed by elution. Therefore, there is no mixing with the platinum group metal recovered as chloride.

[0050] Further, in the present invention, chlorination is performed by mixing with an alkali halide such as sodium chloride or the like and passing a chlorine gas while heating at 500 to 700 ° C., and dissolving it in an aqueous hydrochloric acid solution. That is, since the platinum group metal can be dissolved, it can be recovered, for example, as a mixed chloride containing iridium and ruthenium. Thereby, for example, since titanium, tantalum oxide and all other impurities can be completely separated and removed, it is possible to recover a high-purity platinum group metal with few impurities.

[0051] Also, in the present invention, the hydrochloric acid aqueous solution of the platinum group metal chloride is optionally distilled under reduced pressure to adjust the hydrochloric acid concentration or the platinum group metal concentration, and the platinum group metal chloride or chloride solid is recovered as a solid. be able to.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) C22B 7/00 C22B 3/00 M 11/00 11/04 F term (reference) 4K001 AA41 CA01 CA02 DA08 DA10 DA14 DB04 DB21 DB22 4K058 AA22 BA19 BA37 BB03 CA05 DD13 DD18 DD22

Claims (8)

[Claims] In a method of recovering a platinum group metal from a water-soluble metal electrode having a coating layer containing a platinum group metal oxide, the coating layer is peeled off from an electrode substrate, and the coated sludge is reduced in a reducing atmosphere. After reducing the platinum group metal component to metal by heating in an atmosphere, chlorinating the solution to form an aqueous hydrochloric acid solution, removing the undissolved portion by filtration, and then separating and removing existing cations by electrodialysis using a cation exchange membrane. By doing
A method for recovering a platinum group metal from a metal electrode, wherein the platinum group metal is recovered as a chloride. 2. A method for recovering a platinum group metal from a metal electrode, wherein the peeling of the coating layer according to claim 1 is performed physically and / or chemically. 3. A method for recovering a platinum group metal from a metal metal according to claim 1, wherein the reducing atmosphere is a hydrogen gas atmosphere and the heating temperature is 500 to 1000 ° C. 4. The platinum group metal according to claim 1, wherein the platinum group metal is ruthenium, and the chlorination is performed by dissolving in a heated concentrated hydrochloric acid aqueous solution containing an oxidizing gas. A method of recovering a platinum group metal from a metal electrode. 5. The platinum group metal according to claim 1, wherein the platinum group metal is iridium or iridium / ruthenium.
Heating the chlorination by mixing with the alkali halide;
A method for recovering a platinum group metal from a metal electrode, which is performed by passing chlorine gas. 6. A method for recovering a platinum group metal from a metal electrode, wherein the alkali halide according to claim 5 is sodium chloride and the heating temperature is 500 to 700 ° C. 7. A platinum group from a metal electrode, wherein electrolysis is performed while supplying a solution to an anode chamber using the cation exchange membrane according to claim 1 as a diaphragm, and an impurity metal is sent to a cathode chamber for separation. How to collect electrodes. 8. The method for recovering a platinum group metal from an electrode metal according to claim 1, wherein the concentration treatment is performed by distillation under reduced pressure.